1. Field of the Invention
The present invention relates to an electromagnetic wave measuring apparatus that is suitably applicable to, for example, a case of measuring EMI (Electromagnetic Interference) radiated from an electronic apparatus or the like.
2. Description of the Related Art
From the past, electromagnetic waves radiated from a clock oscillation circuit and the like included in many electronic apparatuses (for example, bundled products such as computer apparatus and recorder), for driving a CPU, a bus, an external memory, and the like, may become a cause of electromagnetic interference (EMI) that disturbs functions of other electronic apparatuses. Therefore, public institutions such as International Special Committee on Radio Interference and American National Standards Institute have established EMI industry standards. Further, government institutions such as Federal Communications Commission (hereinafter, abbreviated as FCC) regulate an EMI level of an electronic apparatus. Hereinafter, the International Special Committee on Radio Interference is abbreviated as CISPR, and the American National Standards Institute as ANSI.
Characteristics of EMI evaluation facilities (referring to open area test site and radio anechoic chamber) are obtained according to NSA (Normalized Site Attenuation) provided by CISPR, ANSI, and the like. At an EMI evaluation facility that meets a condition on a tolerance of an actual measured characteristic with respect to a theoretical value, the tolerance being within ±4 dB, together with various provisions such as GRP (Ground Reference Plane), a regulatory compliance evaluation for each country and control of electronic apparatuses mass-produced are performed. An EMI conformity evaluation is conducted by the following procedure. First, a height of a reception antenna is changed from 1 to 4 m in 360-degree directions of an electronic apparatus and a maximum value of a received electromagnetic wave is acquired. Next, an electric field intensity is calculated by correcting the acquired maximum value of the electromagnetic wave with antenna characteristics and loss of a coaxial cable. Then, it is verified that the electric field intensity falls within a range of predetermined limit values.
FIGS. 19 each show an example of an antenna positioner in related art as an example of an electromagnetic wave measuring apparatus that performs the EMI conformity evaluation.
FIG. 19A shows a first structure example of the antenna positioner in related art.
FIG. 19B shows a second structure example of the antenna positioner in related art.
FIG. 19C shows a third structure example of the antenna positioner in related art.
An antenna positioner 100a (100b, 100c) used to measure an electromagnetic wave generated by an electronic apparatus (hereinafter, also referred to simply as EMI measurement) is installed in an EMI evaluation facility that is used at a time of the EMI conformity evaluation. The antenna positioner 100a (100b, 100c) placed on a flat floor includes an antenna positioner base portion 103a (103b, 103c) that is horizontally movable on the floor. Further, the antenna positioner 100a (100b, 100c) includes an antenna mast 102a (102b, 102c) that is installed in the antenna positioner base portion 103a (103b, 103c) and supports a reception antenna 101a (101b, 101c) that performs the EMI measurement. As the reception antenna 101a (101b, 101c), various types of antennas are used in accordance with types of electronic apparatuses or electromagnetic waves to be measured.
When the antenna positioner base portion 103a (103b, 103c) is stopped at a predetermined position, the reception antenna 101a (101b, 101c) moves vertically to the floor along the antenna mast 102a (102b, 102c). Then, the reception antenna 101a (101b, 101c) is stopped at a desired height and measures an electromagnetic wave generated by the electronic apparatus.
Japanese Utility Model Application Laid-Open No. Hei 05-82117 discloses an antenna ascending/descending and turning apparatus that turns a reception antenna about a horizontal shaft thereof by only 90 degrees and ascends/descends the reception antenna to a necessary height.
Japanese Utility Model Application Laid-Open No. Hei 03-70379 discloses an antenna ascending/descending apparatus that ascends/descends and rotates an antenna and measures an electromagnetic wave.